Flight search site Kayak's chief scientist booked multiple one-way tickets on different airlines for years, finding that this option was often cheaper than booking round trips with the same carrier. Because this method became so commonly effective, they decided to make it a feature of the site.

When you search Kayak for a round trip, you'll find "Hacker Fares" listed in your results. These fares will show you two one-way tickets on different airlines that you can book separately. You don't have to accept these fares, but in the five searches I made I found they were always the cheapest. Loyalty to a specific carrier may earn you rewards points, but if the hacker fares are cheap enough they'll always be a better deal in the long run.

UPDATE: Through a strange chain of events we somehow thought this happened today and was news. Sometimes that happens when you work at a blog! Anyway, sorry for any confusion this may have caused, but if you didn't know about the feature before be sure to check it out. It's still really cool!